At maturity, about 40% of soybean seed dry weight is protein and 20% extractable oil. These constitute the economically valuable products of the soybean crop. Plant oils for example are the most energy-rich biomass available from plants; they have twice the energy content of carbohydrates. It also requires very little energy to extract plant oils and convert them to fuels. Of the remaining 40% of seed weight, about 10% is soluble carbohydrate. The soluble carbohydrate portion contributes little to the economic value of soybean seeds and the main component of the soluble carbohydrate fraction, raffinosaccharides, are deleterious both to processing and to the food value of soybean meal in monogastric animals (Coon et al., (1988) Proceedings Soybean Utilization Alternatives, Univ. of Minnesota, pp. 203-211).
As the pathways of storage compound biosynthesis in seeds are becoming better understood it is clear that it may be possible to modulate the size of the storage compound pools in plant cells by altering the catalytic activity of specific enzymes in the oil, starch and soluble carbohydrate biosynthetic pathways (Taiz L., et al. Plant Physiology; The Benjamin/Cummings Publishing Company: New York, 1991). For example, studies investigating the over-expression of LPAT and DAGAT showed that the final steps acylating the glycerol backbone exert significant control over flux to lipids in seeds. Seed oil content could also be increased in oil-seed rape by overexpression of a yeast glycerol-3-phosphate dehydrogenase, whereas over-expression of the individual genes involved in de novo fatty acid synthesis in the plastid, such as acetyl-CoA carboxylase and fatty acid synthase, did not substantially alter the amount of lipids accumulated (Vigeolas H., et al. Plant Biotechnology J. 5, 431-441 (2007). A low-seed-oil mutant, wrinkled 1, has been identified in Arabidopsis. The mutation apparently causes a deficiency in the seed-specific regulation of carbohydrate metabolism (Focks, Nicole et al., Plant Physiol. (1998), 118(1), 91-101. There is a continued interest in identifying the genes that encode proteins that can modulate the synthesis of storage compounds, such as oil, protein, starch and soluble carbohydrates, in plants.
Serine hydrolase enzymes are abundant in nature and perform different biochemical roles in enzymes such as proteases, lipases, esterases and transferases. All these divergent enzymes share a serine residue in the active site that acts in the nucleophilic attack of the substrate thereby forming a covalent intermediate. Pectin Acetyl esterase (PAE) (EC 3.1.1.6) has been purified from plants and microorganisms. PAE specifically de-acetylates acetylated carbohydrate polymers, such as xylan and pectin. PAE has been shown to remove acetylester groups from, for example, sugar beet pectin at the C2 and/or C3 position of galacturonic acid residues (Nielsen, John E.; Christensen, Tove M. I. E. Distribution of pectin methyl esterase and acetylesterase in the genus Citrus visualized by tissue prints and chromatography. Plant Science (Shannon, Ireland) (2002), 162(5), 799-807.) Genes encoding PAE from plants have been cloned and sequenced (Christensen et al. Protein and cDNA sequences of orange fruit pectin acetylesterase, and uses thereof. PCT Int. Appl. (2000), 88 pp. CODEN: PIXXD2 WO 2000017368 A1 20000330). Large gene families encoding protein with similarity to PAE have been identified in every plant that was subjected to in-depth genome or EST sequencing. The divergent nature of sequences and expression pattern observed for the PAE gene family suggest a biochemical function for gene family members outside of the de-acetylation of polysaccharides. Few studies have been conducted on the possible role of these proteins with similarity to PAE. In view of the ubiquitous nature of genes encoding PAE-like proteins in plants further investigation of their role in plant growth and development and specifically in the regulation of storage compound content in seed is of great interest.